package io.xxx;

// https://leetcode-cn.com/problems/merge-two-sorted-lists/
public class MergeTwoSortedLists {

    public static void main(String[] args) {
        ListNode l1_1 = new ListNode(1);
        ListNode l1_2 = new ListNode(2);
        ListNode l1_3 = new ListNode(4);
        l1_1.next = l1_2;
        l1_2.next = l1_3;
        ListNode l2_1 = new ListNode(1);
        ListNode l2_2 = new ListNode(3);
        ListNode l2_3 = new ListNode(4);
        l2_1.next = l2_2;
        l2_2.next = l2_3;
        ListNode result = mergeTwoLists2(l1_1, l2_1);
        System.out.print("[");
        do {
            System.out.print(result.val);
            result = result.next;
            if (result.next != null) {
                System.out.print(",");
            }
        } while (result.next != null);
        System.out.println("]");
    }

    public static ListNode mergeTwoLists1(ListNode l1, ListNode l2) {
        ListNode head = new ListNode();
        ListNode prev = head;
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                prev.next = l1;
                l1 = l1.next;
            } else {
                prev.next = l2;
                l2 = l2.next;
            }
            prev = prev.next;
        }
        prev.next = l1 == null ? l2 : l1;

        return head.next;
    }

    public static ListNode mergeTwoLists2(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        } else if (l2 == null) {
            return l1;
        } else if (l1.val < l2.val) {
            l1.next = mergeTwoLists2(l1.next, l2);
            return l1;
        } else {
            l2.next = mergeTwoLists2(l1, l2.next);
            return l2;
        }
    }
}

class ListNode {
    int val;
    ListNode next;

    ListNode() {
    }

    ListNode(int val) {
        this.val = val;
    }

    ListNode(int val, ListNode next) {
        this.val = val;
        this.next = next;
    }

    @Override
    public String toString() {
        return "ListNode{" +
                "val=" + val +
                ", next=" + next +
                '}';
    }
}
